Path Selection For A Wireless System With Relays

ABSTRACT

A method selects a path for forwarding a data packet in a wireless communication system. A system capacity versus delay impact curve is calculated for a direct path to mobile station. The direct path has a capacity cost based on communication quality of a direct link between a base station and the mobile station. This curve is shifted by a predetermined time corresponding to an additional delay over a relay path to produce a projected capacity curve for the relay path having a second capacity cost determined according to a combined measure of signal quality of multiple links in the relay path. The second capacity cost is multiplied by a capacity cost ratio to produce a relay capacity curve. The direct path or the relay path is selected based on a comparison of the system capacity versus delay impact curve and the relay capacity curve according to a QoS requirement.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims priority to U.S. ProvisionalApplication Ser. No. 61/022652, filed Jan. 22, 2008, entitled PATHSELECTION FOR A WIRELESS SYSTEM WITH RELAYS, the entirety of which isincorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable

FIELD OF THE INVENTION

The present invention relates generally to a method and system for pathselection and routing and more specifically to a method and system forpath selection for a wireless communication system having relays.

BACKGROUND OF THE INVENTION

When relays are employed in wireless systems, an end user's data andcontrol signals should be communicated with a base station. When amobile station has multiple path options due to the availability ofrelaying stations, communication can be achieved via the direct pathbetween a base station and a mobile station, or via a relay pathinvolving one or more relays between a base, station and a mobilestation. The path taken by the end user's data, and control signals canaffect the performance of the wireless system. The problem ofdetermining which path that end user's data and control signals shouldtake is referred to as the path selection, problem.

Proposals to the Institute of Electrical and Electronics Engineers(“IEEE”) standard 802.16j, submitted prior to the present invention,suggest including the selection of the path based on the overallcapacity impact. For example, if there are two hops and each relay linkcan support equal data rates, for delay tolerant services, it is good toswitch to the relay link only if the relay hops can support at leasttwice the data rate of the direct link to the base station.

However, these proposals do not take into consideration other factorsthat may influence the actual performance of the system and mayincorrectly bias the path selection in favor of one path over another.For example, for certain classes of data and/or services, additionaldelay may not be tolerated and a direct path may be the only viablechoice.

Therefore, what is needed is a system and method for selecting a pathfor routing data packets in a wireless communication system havingrelays which considers data and service parameters in making theselection.

SUMMARY OF THE INVENTION

The present invention advantageously provides a method, apparatus andsystem for routing data packets in a communication system when thecommunication system includes at least one relay station. Datarequirements and system parameters, such as required data rate, type ofservice, user priority, mobility, system loading, fairness, systemloading, added delay and effective data rate may be considered whenselecting a data path.

In accordance with one aspect of the present invention, a method isprovided for selecting a path for forwarding data packets in acommunication system. The communication system includes at least onebase station, at least one relay station and at least one mobilestation. A system capacity versus delay impact curve is calculated for adirect path to a mobile station. The direct path has a first capacitycost determined according to a communication quality of a direct linkbetween a base station and the mobile station. The system capacityversus delay impact curve is shifted a predetermined time to produce aprojected capacity curve for a relay path. The predetermined time delaycorresponds to an additional delay over the relay path. The relay pathincludes the at least one relay station and has a second capacity costdetermined according to a combined measure of signal quality of multiplelinks in the relay path. The second capacity cost is multiplied by acapacity cost ratio to produce a relay capacity carve. Either the directpath or the relay path is selected for forwarding the data packet. Thepath selection is based a comparison of the system capacity versus delayimpact curve and the relay capacity curve at a point in the curvescorresponding to a quality of service requirement of the data packet.

In accordance with another aspect of the present invention, an apparatusfor selecting a path for forwarding data packets in a wirelesscommunication system includes a path selector. The communication systemincludes at least one base station, at least one relay station and atleast one mobile station. The path selector is operable to calculate asystem capacity versus delay impact curve for a direct path to a mobilestation. The direct path has a first capacity cost determined accordingto a communication quality of a direct link between a base station, andthe mobile station. The path selector shifts the system capacity versusdelay impact curve a predetermined time to produce a projected, capacitycurve for a relay path. The predetermined time delay corresponding to anadditional delay over the relay path. The relay path includes the atleast one relay station, and has a second capacity cost determinedaccording to a combined measure of signal quality of multiple links inthe relay path. The path selector further multiplies the second capacitycost by a capacity cost ratio to produce a relay capacity curve andselects one of the direct path and the relay path for forwarding thedata packet. The path selection is based on a comparison of the systemcapacity versus delay impact curve and the relay capacity curve at apoint in the curves corresponding to a quality of service requirement ofthe data packet.

In accordance with yet another aspect of the present invention, awireless communication system includes at least one base station, atleast one mobile station and at least one relay station. The at leastone relay station is communicatively coupled to the at least one basestation. The at least one mobile station is communicatively coupled tothe at least one base station and the at least one relay station. The atleast one mobile station is operable to communicate with the at leastone base station through at least two paths. One path is selected forforwarding a data packet based on a delay requirement of a service flowor the data packet.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof will, be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a block diagram of an exemplary wireless communication systememploying at least one relay, the system constructed in accordance withthe principles of the present invention;

FIG. 2 is a block diagram of an alternative wireless communicationsystem employing at least one relay, the system constructed inaccordance with the principles of the present invention;

FIG. 3 is a block diagram of yet another alternative wirelesscommunication system employing at least one relay, the systemconstructed in accordance with the principles of the present invention;

FIG. 4 is a block diagram of an exemplary mobile station for use in awireless communication system constructed in accordance with theprinciples of the present invention;

FIG. 5 is a block diagram of an exemplary base station of a wirelesscommunication system constructed in accordance with the principles ofthe present invention;

FIG. 6 is a graph illustrating the relationship between system capacityand packet delay (t), constructed in accordance with embodiments of thepresent invention; and

FIG. 7 is a flowchart of an exemplary path selection process performedaccording to the principles of the present invention example ofintermediate indexing.

DETAILED DESCRIPTION OF THE INVENTION

Before describing in detail exemplary embodiments that are in accordancewith the present invention, it is noted that the embodiments resideprimarily in combinations of apparatus components and processing stepsrelated to implementing a system and method for selection a routing pathfor data packets in a wireless communication system. Accordingly, thesystem and method components have been represented where appropriate byconventional symbols in the drawings, showing only those specificdetails that are pertinent to understanding the embodiments of thepresent invention so as not to obscure the disclosure with details thatwill be readily apparent to those of ordinary skill in the art havingthe benefit of the description herein.

As used herein, relational terms, such as “first” and “second,” “top”and “bottom,” and the like, may be used solely to distinguish one entityor element from another entity or element without necessarily requiringor implying any physical or logical relationship or order between suchentities or elements.

One embodiment of the present invention advantageously provides a methodand system for selecting a path for routing data packets that enhancesthe performance of a wireless communication system which employs atleast one relay station. Performance enhancement may be any one orcombination of enhancements to the performance of a wireless system,such as, for example, capacity enhancement, coverage enhancement,mobility enhancement, load balancing situations, etc.

If a service is delay sensitive, switching a mobile station from adirect path to a route having a relay station, such as a two hop system,even if each hop can support more than double the data rate, may bedisadvantageous. This need has not been identified in the related art,and no solutions have been provided prior to the present application.

Additionally, if a mobile station has to send or receive data ormessages with two different Quality of Service (“QoS”) requirements, nosolution has been available to do these communications using differentpaths. In other words, all data would go through the same path.Embodiments of the present invention enable dynamic, semi-static, andstatic path selection, as well as selecting between various kinds ofpath selection.

Referring now to the drawing figures in which like reference designatorsrefer to like elements, there is shown in FIG. 1 an exemplary wirelesscommunication system 10 which employs at least one relay station 12, thewireless system provided in accordance with embodiments of the presentapplication. The wireless communication system 10 includes at least onebase station 14, at least one relay station 12, and at least one mobilestation 16. The mobile station 6 may be a wireless communication devicesuch as a cellular phone, a smart phone, a personal digital assistant(“PDA”), a laptop computer, a desktop computer, an electronic bookreader, or any other device commonly receiving data packets through thebase station 14. Although not shown, base station 14 communicates withother base stations 14 and other external networks via a backbonenetwork.

Several path options exist between base station 14 and mobile station16. First, direct path 18 involves base station 14 and mobile station16. Second, relay path 20 involves base station 14, one or more relaystations 12, and mobile station 16. Third, simultaneous path 22 includesusing direct path 18 simultaneously with relay path 20. FIGS. 2 and 3provide exemplary block diagrams for other exemplary wirelesscommunication systems which employ more than one relay 12. in FIG. 2, nodirect path exists between the base station 14 and the mobile station16; thus, all traffic between the base station 14 and the mobile station16 is routed through one of the two relay stations 12 a, 12 b. In FIG.3, the path options include a direct route 18 between the base station14 and the mobile station 16, as well as alternate routes through one ofthe two relay stations 12 a, 12 b.

In one embodiment of the present invention, one path is selected usingcriteria other than or in addition to the overall capacity impact, andall communications happen in the path selected. However, in anotherembodiment, the impact of the path to the capacity, throughput and delayperformance is determined to depend on the service requirement. Forexample, the path through two relays can incur more delay than a directpath to a mobile station, if available. Therefore, if a mobile station16 has multiple path options, for example, the direct path 18 to thebase station 14, or to connect via a path 20 using a single relaystation 12, or connect to both the mobile station 16 and the relaystation 12 simultaneously via path 22, this decision can beadvantageously made based on the QoS requirements of the service aswell.

When a signal goes through the relay path 20 there can be more delaythan the direct path 18. Therefore, for example, if a mobile station 16initiated a voice service, the additional delay would impact theperformance. The impact of delay may increase if the delay in a wirelinesection of the path is high and close to the tolerable limits, such thatthe delay budget over wireless is very small. In this case, even a smalldelay in the wireless network may impact the performance significantly.

In an alternative embodiment, different services are served viadifferent paths as required so that the QoS of the service is taken intoaccount, i.e., per service based selection. In addition, in anotheralternative embodiment, a technique is provided to select the best pathbased on the service requirements and capacity and coverage impact. Whenswitching, path selection may be accomplished in a dynamic manner whenmultiple QoS data streams are present or in a static manner to fit themost important data/traffic service. The decision to switch may be madein a dynamic manner or static manner based on the delay requirements ofthe individual packet or overall delay requirement of the service. Inaddition, if a mobile station 16 has to send or receive data or messageswith multiple QoS requirements, it is advantageous to send the relateddata through the optimal path for each service, e.g., data or message,which means for the same mobile station 16 there can be multiple pathsselected for communication.

In another alternative embodiment, the path is to be selected based ondelay and/or QoS of the services in addition to the capacity, coverage,and individual access station loading. The path may be selected, on aper service basis for a given mobile station 16 in a dynamic manner,whereby different data streams follow different paths. Alternatively,this switching may be done based on the importance of the data stream ofthe mobile station 16. A way to take into account the delay impact onthe capacity cost, and therefore the impact on overall cost function, isalso provided with an example scheme.

In yet another alternative embodiment, a path is selected based on theQoS of service in addition to the resource cost, i.e., resource usageper data unit, of an individual path. The path selection may allow delaytolerant services to use the path with minimum resource cost.Additionally, as delay sensitive services experience a higher resourcecost when using relays due to the added delay of the relay, the resourcecost due to additional delay is compared with the resource costreduction due to the increased data rate, i.e., additional boost insystem capacity. A method to select the best path considers the resourcecost due to additional packet delay. The path selection may be dynamic,semi-static, or static.

Referring now to FIG. 4, an exemplary block diagram of mobile station 16useful for implementing an embodiment of the present invention isprovided. Mobile station 16, in an exemplary system 10, includes one ormore processors, such as processor 24. The processor 24 is connected toa communication infrastructure 26, e.g., a communications bus, cross-barinterconnect, network, etc. Mobile stations 16 can optionally include orshare a display interface 28 that forwards graphics, text, and otherdata from the communication infrastructure 26 for display on a displayunit 30. The mobile station 16 also includes a main memory 32,preferably random access memory (“RAM”), and may also include asecondary memory 34. Although most often implemented as part of a basestation 14, the main memory 32 may include a path selector 36 fordetermining a desired path for routing data packets through the system10. The path selector 36 is discussed in greater detail below.

The secondary memory 34 may include, for example, a hard disk driveand/or a removable storage drive, representing a floppy disk drive, amagnetic tape drive, an optical disk drive, etc. The removable storagedrive reads from and/or writes to a removable storage unit 38 in amanner well known to those having ordinary skill in the art. Removablestorage unit 38, represents, for example, a floppy disk, magnetic tape,optical disk, etc. which is read by and written to by secondary memory34. As will be appreciated, the removable storage unit 38 includes acomputer usable storage medium having stored therein computer softwareand/or data.

In alternative embodiments, the secondary memory 34 may include othersimilar means for allowing computer programs or other instructions to beloaded into the computer system. Such means may include, for example, aremovable storage unit 38 and an interface (not shown). Examples of suchmay include a program cartridge and cartridge interface (such as thatfound, in video game devices), a removable memory chip (such as anEPROM, EEPROM or PROM) and associated socket, and other removablestorage units 38 and interfaces which allow software and data to betransferred from the removable storage unit 38 to the mobile station 16.

In this document, the terms “computer program medium,” “computer usablemedium,” and “computer readable medium” are used to generally refer tomedia such as but not limited to main memory 32, secondary memory 34,removable storage unit 38, a hard disk installed in hard disk drive,etc. These computer program products are means for providing software tothe mobile station 16. The computer readable medium allows the mobilestation 16 to read data, instructions, messages or message packets, andother computer readable information from the computer readable medium.The computer readable medium, for example, may include non-volatilememory, such as floppy, ROM, flash memory, disk drive memory, CD-ROM,and other permanent storage. It is useful for example, for transportinginformation, such as data and computer instructions, between otherdevices within system 10.

Computer programs (also called computer control logic) are stored inmain memory 32 and/or secondary memory 34. Computer programs may also bereceived via a transceiver 40. Such computer programs, when executed,enable the mobile station 16 to perform the features of the presentinvention as discussed herein. In particular, the computer programs,when executed, enable the processor 24 to perform the features of thecorresponding mobile station 16. Accordingly, such computer programsrepresent controllers of the corresponding device.

Mobile station 16 may also include an Input/Output (“I/O”), interface42, I/O interface 42 allows mobile station 16 to present information toand accept data from a user through a variety of input/output devices,e.g., keyboard, mouse, touch screen, buttons, microphone, speaker, USBdevices, etc. Information transferred via I/O interface 42 are in theform of signals which may be, for example, electronic, electromagnetic,optical, or other signals capable of being received by I/O interface 42.

The transceiver 40 transmits and receives wireless communication signalsencoded in accordance with defined communication protocol standards,including but not limited to, Code division multiple access (“CDMA”),Time division multiple access (“TDMA”), Global System for MobileCommunications (“GSM”), Enhanced Data rates for GSM Evolution (“EDGE”),Evolution-Data Optimized (“EVDO”), Third Generation (“3G”), Long-termEvolution (“LTE”), Wi-Fi, WiMAX, etc. Transceiver 40 is electricallyconnected to an encoder/decoder 44 which decodes and encodes datapackets according to a predefined encryption scheme.

Referring now to FIG. 5, a block diagram of an exemplary base station 14is provided. It should be noted that while FIG. 5 details only thefeatures relevant to the present invention, other features and functionsof a typical base station 14 may be included, as is well-known to thoseof ordinary skill in the art.

Base station 14 receives and transmits wireless communication signalsencoded in accordance with defined communication protocol standards viaan antenna 46 coupled to a transceiver 48. The transceiver 48 is coupledto an encoder/decoder 50 which encrypts raw data packets prior totransmission and decrypts received data packets for interpretation by aprocessor 52.

The processor 52 controls the operation of the base station 14 and theflow of data within the base station 14 and controls the execution ofthe functions described herein. The base station 14 also includes a mainmemory 54, preferably random access memory (“RAM”), and may also includea secondary memory 56. The main memory 54 includes a path selector 58for determining a desired path for routing data through the system 10.

The secondary memory 56 may include, for example, a hard disk driveand/or a removable storage drive, representing a floppy disk drive, amagnetic tape drive, an optical disk drive, etc. The removable storagedrive reads from and/or writes to a removable storage unit 59 in amanner well known to those having ordinary skill in the art. Removablestorage unit 59, represents, for example, a floppy disk, magnetic tape,optical disk, etc. which is read by and written to by secondary memory56. As will be appreciated, the removable storage unit 59 includes acomputer usable storage medium having stored therein computer softwareand/or data.

The processor 52 is further electrically connected to a communicationinterface 60. Communication interface 60 allows software and data to betransferred between the base station 14 and external devices, includinga public-switched telephone network (“PSTN”), Internet, etc. (notshown). Examples of communication interface 60 may include a modem, anetwork interface (such as an Ethernet card), a communications port, aPCMCIA slot and card, etc. Software and data transferred viacommunication interface 60 are in the form of signals which may be, forexample, electronic, electromagnetic, optical, or other signals capableof being received by communication interface 60.

Referring now to FIG, 6, a graph is provided which illustrates therelationship between System Capacity and Packet Delay (t) for the casewhere two paths for routing data exist; direct path 18 and relay path20, as shown in FIG. 1. Assuming for a given mobile, K₁ and K₂ areresource units per data unit, i.e., resource cost, for direct and relaypaths respectively. The capacity cost ratio, K_(r), of resource costgain of relay path relative to the direct path is shown by therelationship K_(r)=K₂K₁. For example, if the relay path needs two timeslots and uses the same data rate, i.e. modulation and coding scheme(“MCS”), then K_(r)=2 neglecting additional overhead. If the relay pathdata rate is doubled and use two time slots, i.e., higher MCS, K_(r)=1.If the system capacity is the only criterion to be used foroptimization, then the path decision can be described as, if K_(r)<1 userelay path; else, use direct path.

If packet delay impact is also taken into consideration, then assumerelay path incurs T additional delay for all connections. This exampleis true if there is no variable queuing/scheduling delay involved in therelay, e.g., in centralized store and forward type of relays. In thecase of variable delay, the estimated average additional delay at therelay for a particular type data may be assessed.

Referring now to FIG. 7, an exemplary operational flowchart is providedthat describes steps performed by a path selector 36, 58 for selecting apath for routing data packets in a wireless communication system havingrelays. The process allows different paths to be selected for individualdata packets for a variety of scenarios. For example, control packetsand data packets may have different delay requirements and differentapplication packets may have different delay requirements. Additionally,the uplink (“UL”) and downlink (“DL”) may have different delayrequirements and therefore choose different paths.

The process begins by finding the capacity vs delay impact curve withoutrelay (step S102), i.e., C1(t) curve 62 in FIG. 6. The capacity vs delayimpact curve without relay 62 may be found, for example, usingsimulations. The capacity vs delay impact curve without relay 62 isshifted by time, T (step S104), to get the projected curve 64, C2(t),where C2(t)=C1(t−T), for relay having the same capacity cost, i.e.,K_(r)=1. Depending on the mobile, the normalized capacity cost for relaypath may be higher or lower than 1. For such a mobile, the capacitycurve 66, C3(t), where C3(t)=Kr*C2(t), can be obtained by multiplyingC2(t) by Kr (step 106).

A path is selected based on the service requirements, including but notlimited to, the required data rate, type of service, added delay, etc.(step S108). However, when other factors such as system loading andfairness are to be taken into consideration, these service requirementsare used not to select the path, but to bias the decision appropriatelytowards or against selecting the path. For example, higher loading inthe relay path may completely prohibit, the selection of a path althoughthat path is more advantageous in terms of resources and performance. Onthe other hand, due to the loading changes, a particular service may bemoved to the direct path to admit a different favorable service. Becauseof the extra delay in the relay system, there is a capacity penalty.When providing a t1 packet delay, the capacity of the relay system wouldreduce to Cr which corresponds to a service with packet delay of t1−T.The capacity penalty ratio Kd=C/Cr, when Kd≧1. Overall capacity when therelay path provides a service with t1 delay is given by Kr*Cr Therefore,the relay path should be selected when Kr*Cr>C or Kr/Kd>1, where Kr isthe resource usage gain for a given mobile and Kd is the capacitypenalty due to delay for that service, and when no other factor needs tobe considered, e.g. loading of each node/path, handover penalties, etc.When other Factors are also needed to be considered, the selectionshould be appropriately weighted by this factor to make the finaldecision.

If the required data rate can only be provided by the direct link, thedirect link is used. Likewise, if only the relay link can provide acertain data rate for coverage enhancement, the mobile station 16 needsto be served by the relay. However, if a given service can be served bytwo paths, e.g. direct and relayed path, two situations exist. First, ifthe delay is not a concern, the path can be selected based on theminimum resource usage per data unit, which maximizes capacity or anyother selected criterion, such as individual station loading, But, fordelay sensitive data, additional delay incurred when relaying may impactthe performance or the resource cost.

A path is selected based on the service requirement as well. Embodimentsof the present invention provide path selection wherein several modes ofoperation are enabled, including dynamic path selection, semi-staticpath selection and static path selection for both delay tolerant data aswell as delay sensitive data. For dynamic path selection, packetsbelonging to the same mobile station 16, and the same service can takedifferent paths to/from base station 14 based on packet delay and size.For semi-static path selection, different data streams having differentQoS, but belonging to the same mobile station 16, may use differentpaths to/from the base station 14 based on the service requirements. Forstatic path selection, a mobile station 16 is assigned a path based onoverall service requirements, i.e., two mobiles in the same locationwith different service requirements may use two different paths. Forexample, with delay tolerant data, the selection may be based only oneffective data rates of two paths, e.g., capacity/coverage impact,mobility and system loading. However, for delay sensitive data, theoverall best path is selected based on above factors, as well as thedelay impact, and this path does not change.

The impact of delay may increase if the delay in the wireline section ishigh, which reduces the wireless delay budget. Evert a small delay inthe wireless network may impact the performance significantly.

With dynamic path selection, where packets belong to the same mobilestation 16 and the same service can take different paths to/from basestation 14 based on packet delay and size, for the downlink, theremaining delay budget of a packet depends on the delay already incurredin the wireline system, which is a variable. Therefore, depending on theremaining delay budget, the scheduler can decide to send the packet viadirect or relay link, on a dynamic basis. For the uplink, if thewireline delay can be estimated using congestion data, this delay may beused to dynamically send data via direct or relay link.

Delay cost is mapped to the capacity cost as a linear relationship. Oncedelay cost is estimated, this cost may be used in any optimizationalgorithm, involving many other factors such as system loading,individual data rate, system fairness, mobility, system capacity,priority and coverage.

The capacity cost may be calculated according to several methods, usingmany factors, such as, but not limited to, user priority. For example,capacity cost may be a function of mobility, system loading, fairness,delay, data rate. Alternatively, capacity cost may be a function ofmobility, system loading, fairness, delay, multiplied by an effectivedata rate. Additionally, capacity cost may be a function of mobility,system loading, fairness, multiplied by a delay cost as well as aneffective-data rate. Calculating capacity cost considering mobilityimpact, system loading and fairness has already been discussed above.

In view of FIGS. 1, 2 and 3, a person, of ordinary skill in the art isenabled to extend the techniques presented herein by induction towireless systems which employ any number of relay stations, such as butnot limited to wireless Mesh networks.

The present invention can be realized in hardware, software, or acombination of hardware and software. Any kind of computing system, orother apparatus adapted for carrying out the methods described herein,is suited to perform the functions described herein.

A typical combination of hardware and software could be a specialized orgeneral purpose computer system having one or more processing elementsand a computer program stored on a storage medium that, when loaded andexecuted, controls the computer system such that it carries out themethods described herein. The present invention can also be embedded ina computer program product, which comprises all the features enablingthe implementation of the methods described herein, and which, whenloaded in a computing system is able to carry out these methods. Storagemedium refers to any volatile or non-volatile storage device.

Computer program or application in the present context means anyexpression, in any language, code or notation, of a set of instructionsintended to cause a system having an information processing capabilityto perform a particular function either directly or after either or bothof the following a) conversion to another language, code or notation; b)reproduction in a different material form.

In addition, unless mention was made above to the contrary, it should benoted that all of the accompanying drawings are not to scale.Significantly, this invention can be embodied in other specific formswithout departing from the spirit or essential attributes thereof, andaccordingly, reference should be had to the following claims, ratherthan to the foregoing specification, as indicating the scope of theinvention.

1. A method of selecting a path for forwarding a data packet in awireless communication system, the wireless communication system,including at least one base station, at least one relay station and atleast one mobile station, the method comprising: calculating a systemcapacity versus delay impact curve for a direct path to a mobilestation, the direct path having a first capacity cost determinedaccording to a communication quality of a direct link between a basestation and the mobile station; shifting the system capacity versusdelay impact curve by a predetermined time to produce a projectedcapacity curve for a relay path, the predetermined time delaycorresponding to an additional delay over the relay path, the relay pathincluding the at least one relay station and having a second capacitycost determined according to a combined measure of signal quality ofmultiple links in the relay path; multiplying the second capacity costby a capacity cost ratio to produce a relay capacity curve; andselecting one of the direct path and the relay path for forwarding thedata packet, the path selection based a comparison of the systemcapacity versus delay impact curve and the relay capacity curve at apoint in the curves corresponding to a quality of service requirement ofthe data packet.
 2. The method of claim 1, wherein the path selection isfurther based on at least one of a required data rate, a type ofservice, user priority, mobility, system loading, fairness, systemloading, and an effective data rate.
 3. The method of claim 1, whereinthe path selection is further based on a modified combined index basedon at least one of a required data rate, a type of service, userpriority, mobility, system loading, fairness, system loading, and aneffective data rate, the modified combined index created by biasing thepath selection in consideration of additional capacity cost and delayimpact.
 4. The method of claim 1, wherein the relay path is selected forthe mobile station when a ratio of a resource usage gain for the mobilestation and a capacity penalty is greater than
 1. 5. The method of claim1, wherein the path selection is one of a dynamic path selection, asemi-static path selection, and a static path selection.
 6. The methodof claim 5, wherein the path selection is a dynamic path selection, thedirect path and the relay path are dynamically selectable for forwardingthe data packet corresponding to a same mobile station and having a samequality of service.
 7. The method of claim 6, wherein the one of thedirect path and the relay path is selected based on a traffic patternand a quality of service requirement.
 8. The method of claim 5, whereinthe path selection is a semi-static path selection, the direct path andthe relay path are dynamically selectable for forwarding the data packetcorresponding to a same mobile station and having multiple service flowswith differing qualities of service.
 9. The method of claim 5, whereinthe path selection is a static path selection, the one of the directpath and the relay path is selected based on an effective data rate ofeach path and a quality of service requirement.
 10. An apparatus forselecting a path for forwarding a data packet in a wirelesscommunication system, the wireless communication system including atleast one base station, at least one relay station and at least onemobile station, the apparatus comprising: a path selector operable to:calculate a system capacity versus delay impact curve for a direct pathto a mobile station, the direct path having a first capacity costdetermined according to a communication quality of a direct link betweena base station and the mobile station; shift the system capacity versusdelay impact curve a predetermined time to produce a projected capacitycurve for a relay path, the predetermined time delay corresponding to anadditional delay over the relay path, the relay path including the atleast one relay station and having a second capacity cost determinedaccording to a combined measure of signal quality of multiple links inthe relay path: multiply the second capacity cost by a capacity costratio to produce a relay capacity curve; and select one of the directpath and the relay path for forwarding the data packet, the pathselection based on a comparison of the system capacity versus delayimpact curve and the relay capacity curve at a point in the curvescorresponding to a quality of service requirement of the data packet.11. The apparatus of claim 10, wherein the path selection is furtherbased on at least one of a required data rate, a type of service, userpriority, mobility, system loading, fairness, system loading, and aneffective data rate.
 12. The apparatus of claim 10, wherein the pathselection is further based on a modified combined index based on atleast one of a required data rate, a type of service, user priority,mobility, system loading, fairness, system loading, and an effectivedata rate, the modified combined index created by biasing the pathselection in consideration of additional capacity cost and delay impact.13. The apparatus of claim 10, wherein path selector selects the relaypath for the mobile station when a ratio of a resource usage gain forthe mobile station and a capacity penalty is greater than
 1. 14. Theapparatus of claim 10, wherein the path selection is one of a dynamicpath selection, a semi-static path selection and a static pathselection.
 15. The apparatus of claim 14, wherein the path selection isa dynamic path selection, the direct path and the relay path aredynamically selectable for forwarding the data packets corresponding toa same mobile station and having a same quality of service.
 16. Theapparatus of claim 15, wherein the one of the direct path and the relaypath is selected based on a traffic pattern and a quality of servicerequirement.
 17. The apparatus of claim 14, wherein the path selectionis a semi-static path selection, the direct path and the relay path aredynamically selectable for forwarding data packets corresponding to asame mobile station and having multiple service flows with differingqualities of service.
 18. The apparatus of claim 14, wherein the pathselection is a static path selection, the one of the direct path and therelay path is selected based on an effective data rate of each path anda quality of service requirement.
 19. A wireless communication systemcomprising: at least one base station; at least one relay stationcommunicatively coupled to the at least one base station; and at leastone mobile station communicatively coupled to the at least one basestation and the at least one relay station, the at least one mobilestation operable to communicate with the at least one base stationthrough at least two paths, a selected path of the at least two pathsselected for forwarding a data packet based on a delay requirement of atleast one of a service flow and the data packet.
 20. The wirelesscommunication system of claim 19, wherein the at least one base stationincludes: a path selector operable to: calculate a system capacityversus delay impact curve for a first path to a mobile station, thefirst path having a first capacity cost determined according to acommunication quality of a direct link between a base station and themobile station; shift the system capacity versus delay impact curve by apredetermined time to produce a projected capacity curve for a secondpath, the predetermined time delay corresponding to an additional delayover the second path, the second path having a second capacity cost,determined according to a combined measure of signal quality of multiplelinks in the second path; multiply the second capacity cost by acapacity cost ratio to produce a relay capacity curve; and select one ofthe first path and the second path for forwarding the data packet, thepath selection based on a comparison of the system capacity versus delayimpact curve and the relay capacity curve at a point in the curvescorresponding to a quality of service requirement of the data packet.